Abstract: AimTo study the effects of indomethacin on interleukin-6 (IL-6) expression stimulated with lipopolysaccharide （LPS）in rheumatoid arthritic patients' synoviocyte. MethodsFibroblast-like cells (FLS) from rheumatoid arthritic patients' joint tissue were cultured for 24 h and incubated 24 h with LPS (1 mg·L^-1) or the supernatant of U937 cells stimulated by LPS (1 mg·L^-1) . After indomethacin or dexamethasone added into the supernatant of U937 cells, FLS was incubated with the super natant for 24 h. The expression of IL-6 protein was detected by radioimmunoassay. The mRNA expression of IL-6 was accessed by RT-PCR. ResultsLPS did not obviously affect the growth of FLS, and the protein secretion and mRNA expression of IL-6 were not changed in FLS treated with LPS. The IL-6 secretion and IL-6 mRNA expression were significantly increased in FLS cultured with the supernatant from U937 cell treated with LPS. Indomethacin at concentrations of 1×10^-7-1×10^-5 mol·L^-1 obviously inhibited the protein secretion and mRNA expression of IL-6 in FLS cultured with the supernatant from U937 cell stimulated with LPS, and the inhibitory effects increased as the concentrations of indomethacin increased. ConclusionIndomethacin can inhibit the increase of IL-6 expression caused by supernatant of U937 cells stimulated with LPS in FLS.